These saved me from a redesign 25 years ago. I had an 8051 with 256 bytes of RAM and a serial EEPROM with limited writes. Replacing the EEPROM with a serial FRAM allowed me to increase the effective RAM. I had to do some tweaking and figuring because it was so much slower. Also, FRAMs had limited writes AND reads, but on the order of billions instead of millions. Billions of reads are a lot, but you still had to be careful.